Networks with sensors for air safety and security

ABSTRACT

Airborne particles are impacted on a collection surface, analyzed, and then the collection surface is regenerated. Thus, the same collection surface can be used in numerous cycles. The analysis can be focused on one or more properties of interest, such as the concentration of airborne biologicals. Sensors based on regenerative collection surfaces may be incorporated in many networks for applications such as building automation.

FIELD OF INVENTION

The invention relates to methods and devices for continuous monitoringof airborne particles, airborne biological particles, and systems ofmonitoring air quality.

BACKGROUND OF INVENTION

Monitoring airborne particles is of concern in a number of civilian andmilitary contexts. Airborne hazards can come in a variety of forms, forexample, of biological, chemical, or radiological nature. Sometimessevere biological airborne perils may suddenly arise at unpredictablelocations, such as in bio-terrorist attacks. The most efficient responseto biohazards can be mounted based on their earliest practicabledetection.

The typical problem facing the aerosol field is that of collecting andcharacterizing airborne particles. Characterization of these airborneparticles can be performed in situ (i.e., while the particles remainsuspended in a gas), or in extractive techniques where particles arecollected and then deposited onto a solid substrate or into a liquid forthe purpose of subsequent physical or chemical analysis.

Identifying biological materials in situ has been attempted by detectionof autofluorescence of airborne bacteria. While autofluorescentproperties may be useful in detecting biological particles, their insitu measurement is challenging for a number of reasons. It isparticularly difficult to measure fluorescent characteristics ofminuscule particles in an airborne state. The particles are availablefor analysis quite briefly, thus making it difficult to determineseveral informative characteristics. In addition, the equipment requiredcomprises expensive powerful lasers and sensitive fluorescencephotodetectors or photon counters. The resulting devices are large andexpensive, making this technology unlikely to be adopted for someapplications, such as routine monitoring of civilian buildings.

In alternative approaches, extractive instruments such as jet impingers,jet impactors, cyclones, and filters deposit particles onto substrates,which may be liquids, surfaces such as greased slides or agar-coatedplates, or filters. The content of extracted particles can then beanalyzed by any desirable technique. While analysis of airborneparticles may be performed more thoroughly with extractive rather thanin situ techniques, extractive techniques require consumables such asdeposit substrates and/or analysis reagents and/or human involvement inthe analysis. Continuous use of consumables and/or labor can becomeproblematical and prohibitively expensive. Therefore, monitoring systemsbased on extractive techniques are also of questionable value forroutine, continuous use.

There is a current need for devices and methods to continuously detectairborne particles. Continuous monitoring of the largest possible numberof populated premises seems the most desirable option in dealing withthe unpredictability of airborne biohazards emergence. Widespreadadoption of such devices would allow protection of a large number ofpotentially endangered persons. For widespread adoption, however, suchdevices should be fairly inexpensive and reliable. Operation of thedevice should be automatic, i.e. not requiring any user input. Inaddition, to be used routinely in a large number of buildings airbornebiohazard detection devices should ideally be maintenance free and useno consumables.

SUMMARY OF INVENTION

In one aspect the present invention relates to methods for continuouslymonitoring airborne particles. Continuous monitoring according to theinvented methods is achieved through a plurality of cycles. The methodsare suitable for monitoring a variety of airborne particles. In specificembodiments they are designed to monitor the presence or concentrationof airborne hazards. Cycles according to the invented methods comprise aplurality of steps.

A step according to the present methods is depositing airborne particleson a collection surface. Accordingly, a spot is formed on the collectionsurface. Depositing airborne particles is preferably accomplished byimpaction caused by directing an air stream at the collection surface.In a preferred embodiment, airborne particles in the 0.5-10 μm sizerange are retained in the spot, the airborne particles retained in thespot thus comprising biological particles. Some embodiments comprise theoptional step of pre-concentrating airborne particles of a desirablesize range, such as particles with sizes between about 0.5-10 μm, in theair stream prior to impaction on the collection surface. Someembodiments comprise the optional step of preconditioning the air streamby removing particles of an undesirably large size. For example,particles of sizes greater than 10 μm may be removed. In someembodiments, both preconditioning and pre-concentrating are performed,with the pre-conditioning preferably prior to the pre-concentratingstep.

In some embodiments, a step prior to depositing airborne particles ismoistening the collection surface. Many types of liquids may be used tomoisten the collection surface including glycerol, alcohols, or mediumweight hydrocarbons, such as octane. The precise volume of liquid usedin each cycle depends on several different variables, but may be about 5μl.

Another step of the invented methods comprises analyzing the spot. Thetype of analysis performed depends on the nature of the particles to bemonitored. Preferably, analyzing is accomplished by measuringbiological, chemical, and/or radiological properties of the spot. Insome embodiments, a plurality of properties is measured for eachcollected spot. Appropriate measurements in various embodiments may bedirected to fluorescence, infrared absorption, mass specter, Ramanspecter, gamma emission, alpha emission, or beta emission properties ofthe spot. In preferred embodiments, biological particles are monitoredby measuring autofluorescence of the spot. In some embodiments,analyzing is preceded by an optional step of pre-treating the spot so asto enhance the measured signal. Thus, pre-treating may comprise addingto the spot a liquid comprising an analysis-enhancing compound, orplasma lysing. In some embodiments where analyzing is accomplished byMatrix Assisted Laser Desorption Ionization (MALDI) time-of-flight massspectrometry, pre-treating may be performed by plasma lysing and addingmatrix solution to the spot.

Another step of the invented methods comprises regenerating thecollection surface. As a result of this step the spot is removed and thecollection surface is made available for another cycle. Regeneration isachieved by any one or combination of steps. For example, in someembodiments, regeneration is accomplished by pressing a felt pad againstthe collection surface and moving the felt pad over the collectionsurface. In other embodiments a felt wheel is rotated while pressedagainst the collection surface. In other embodiments the collectionsurface is electrostatically charged as part of the regeneration step.In other embodiments regeneration is accomplished by brushing thecollection surface with a brush. In other embodiments regeneration isaccomplished by blowing an air jet at high velocity towards thecollection surface. In other embodiments, regeneration is accomplishedby scraping the collection surface with a blade. In other embodiments,regeneration is achieved with heat, electricity, lasers or other formsof energy directed at the regenerative surface.

In some embodiments all the cycles of the invented methods areidentical, whereas in other embodiments cycles may comprise differentsteps. In some embodiments, the invented methods in at least a subset ofcycles comprise verifying the regeneration of the surface. Accordingly,the collection surface is analyzed after regeneration (the regeneratedcollection surface) essentially by the same process of analyzing thespot. Thus a background signal level is obtained for the regeneratedsurface. For example, if analyzing the spot is by measuring itsfluorescence properties, verifying may be by similarly measuring thefluorescence properties of the regenerated collection surface to obtaina background fluorescence level. The background signal level is thencompared to predetermined criteria. If the background level is found tobe higher than desirable, regeneration and verification is repeateduntil the background signal level meets predetermined criteria.Alternatively, verifying may employ a test different from that used inthe analysis step.

In other aspects, the present invention relates to devices useful forcontinuously monitoring airborne particles. In different embodiments thedevices serve to monitor of the presence and concentration of airbornehazards for example of a biological, chemical, or radiological nature.The devices comprise several components, which are present in differentcombinations in different embodiments.

One component of the invented devices is an impaction plate. One of itsfeatures is a collection surface, on which a spot of airborne particlesgets collected when the devices are in operation. In some embodiments,the collection surface is smooth, and is therefore easily cleaned by asurface regenerator. In other embodiments, the collection surfacecomprises features that improve the collection efficiency of impactingairborne particles, such as pyramid-shaped structures of about 1-10 μmin height and width. In some embodiments, the impaction plate comprisesmore than one, i.e. a plurality of collection surfaces.

Another component of the invented devices is a spotting nozzle. Thespotting nozzle directs an air stream towards the collection surface ofthe impaction plate. The resulting impact of the air stream produces aspot that contains airborne particles on the collection surface. In someembodiments a particle concentrator, such as a virtual impactor, isplaced upstream of the spotting nozzle, which increases theconcentration of airborne particles within a desirable size range. Insome embodiments, a size selective inlet is placed upstream of thespotting nozzle, which eliminates airborne particles greater than adesirable size. In some embodiments, both a concentrator and a sizeselective inlet are present upstream of the spotting nozzle. In someembodiments the spotting nozzle is substantially vertical while thecollection surface is substantially horizontal. In preferred embodimentsthe nozzle, impaction surface and air stream velocity are configured sothat the spot is enriched in particles of about 0.5-10 μm sizes.

Another component of the invented devices is an analyzer, which canexamine characteristics of the spot on the collection surface. Inpreferred embodiments the analyzer is a fluorescence detector thatdetermines the intrinsic fluorescence characteristics of the spot. Inother embodiments, the analyzer may be for example, an infraredabsorbance detector, a mass spectrometer, a Raman spectrometer. Someembodiments comprise more than one analyzer. Thus, any means foranalyzing the spot suitable for detecting a class of airborne particlesmay be employed.

In some embodiments, the invented devices comprise a pre-analysis spotpreparation station. At this point the spot is prepared to enhance itscharacteristics measured by the analyzer. For example, the spot may becombined with compounds that affect measured properties of the airborneparticles of interest by squirting a liquid containing the appropriatecompound from an inkjet type of device. In one embodiment, thepre-analysis spot preparation station applies a plasma lysis pulse tothe spot, which is then analyzed by MALDI mass spectrometry.

Another component of the present devices is a surface regenerator. Thiscomponent removes the spot from the collection surface during operationof the devices, thus regenerating the surface. In some embodiments theregenerator is a felt pad that regenerates the collection surface bypressing against the collection surface while the pad and the collectionsurface move relative to each other. In some embodiments, the surfaceregenerator is a felt wheel that is pressed against the collectionsurface and simultaneously rotated by a coupled motor. In someembodiments the regenerator is a blade that regenerates the collectionsurface by scraping or wiping it. In some embodiments the surfaceregenerator is a brush that regenerates the surface by brushing orsweeping it. In some embodiments the surface regenerator is aregenerator nozzle that blows air at high velocity towards thecollection surface, preferably at an angle. In some embodiments, theregenerator comprises means for electrostatically charging thecollection surface, which loosens an attached spot. The regenerator maycomprise any means for directing energy to the spot and/or collectionsurface. Useful energy forms include heat, electricity, or lasers. Someembodiments comprise more than one surface regenerator, which may be ofsimilar or different types. Thus, any means for regenerating thecollection surface may be employed.

Another component present in some embodiments is a liquid coatingapplicator. It moistens the collection surface prior to impaction of theairstream, and thus helps trapping airborne particles and enhances thecollection efficiency. The liquid coating applicator may be, forexample, a felt tip pen. It might alternatively be similar to inkjetprinting devices. It comprises a reservoir of liquid to be applied tothe collection surface. There are several types of liquids that may beused, including alcohol, glycerol, or a medium weight hydrocarbon suchas octane.

Another component of the devices is a homing sensor. Its function is tooperatively position the collection surface to the various devicecomponents present in different embodiments, including the liquidcoating applicator if present, the spotting nozzle, the pre-analysisspot preparation station if present, the analyzer, and the surfaceregenerator. Thus, in operation the homing sensor can cyclicallyposition the collection surface sequentially from the liquid coatingapplicator if present to the spotting nozzle to the analyzer, to thepre-analysis spot preparation station, and to the surface regenerator.In general, the invented devices may accomplish the function ofpositioning the collection surface to each present component by anymeans for translocating the collection surface relative to the otherdevice components. For example, a prime mover may be coupled to a shaftto which the impaction plate is attached, and proper positioning of thecollection surface is accomplished by rotation of the shaft atpredefined angles.

The different components of the invented devices can take various shapesin specific embodiments. For example, the homing sensor may comprise ashaft attached to the impaction plate. A prime mover is coupled to theshaft, and the homing sensor functions by rotating the disk atpredefined angles. Each rotation step operatively positions thecollection surface to a component of the devices. In some embodiments,the impaction plate is a disk, and a shaft is positioned along the diskaxis and bound to the disk. In another preferred embodiment, theimpaction plate is a lobed cam, and the impaction surfaces on the sideof the cam. The impaction surfaces are flat, and may be produceddirectly on the cam or created by flat inserts embedded in the cam. Thepreferred material for the insert is a material of high surfacehardness, such as hard-anodized steel, quartz or sapphire.

In another aspect, the present invention relates to devices useful fordetecting or measuring airborne biological particles. The devices maycomprise a collection surface, typically a regenerative collectionsurface, which supports a spot of immobilized airborne particles. Inmany embodiments, the devices further comprise an inertial impactor thatimmobilizes the spot on the collection surface.

The invented devices comprise a detector that is capable of analyzingthe content of the spot. Typically, the detector is capable of sensing abiological signature that is present in the spot. The biologicalsignature is preferably autofluorescence of biomolecules, but any otherknown signature may be sensed, including various types of Raman,infrared absorption, or mass spectra. These biological signatures aredetected with known devices such as fluorescence detectors, Ramanspectrometers, Fourier transform infrared spectrometers, or MALDI massspectrometers. In some embodiments, multiple detectors analyze the spot.As a result of analysis, the detector produces signals, typicallyelectrical signals, which are indicative of the biological signature.Consequently, the detector may recognize the presence of specificbiological materials or may measure the concentration of classes ofbiological materials.

Preferably, the detector is a fluorescence detector that measures theinherent fluorescence of biological particles. The fluorescence detectorcomprises an excitation light source, which emits an excitatoryradiation towards the spot to be analyzed. Any available source ofradiation may be used. In some embodiments, the excitation light sourceis a LED. The excitatory radiation is of wavelengths operative to excitebiomolecules to produce fluorescence. In many embodiments, theexcitatory radiation is substantially ultraviolet, and the fluorescenceradiation may be substantially visible. For example, the excitatorywavelength may be within the 340-370 nm range, or it may beapproximately 266 nm, or it may be approximately 400 nm.

Fluorescence detectors also comprise fluorescence photosensors, whichmeasure the radiation emitted from the spot in response to excitation.Any available photosensor may be used. In some embodiments, thefluorescence photosensor is a photodiode. Fluorescence detectors mayalso comprise additional components, such as a dichroic mirror thatsubstantially reflects excitatory radiation and is substantiallytransparent to fluorescence radiation. The dichroic mirror can bepositioned to reflect the excitatory radiation towards the spot, andallow passage of the emission radiation to the photosensor. Otheroptical components may also be employed, such as an excitation filterpositioned between the excitation light source and the dichroic mirroror spot, and an emission filter positioned between the dichroic mirroror spot and the fluorescence photosensor.

As mentioned above, the detector produces signals related to thebiological signature detected. The signals are usually transmitted to areceiver, which may then relay the signals for further processing. Thesignals typically reach a processor, which may be a computer or a NeuronChip®. The processor is capable to process or interpret the signals andthus establish or gauge the concentration of biological particles in thespot. Consequently, the processor is capable to establish when theconcentration of biological particles in the spot exceeds apredetermined value. In such a case, the processor outputs an alarmsignal that alerts users of the presence of potentially harmful levelsof airborne biological particles.

In yet another aspect, the present invention is related to methods ofdetecting specific airborne particles or concentrations of airbornebiologicals. The methods comprise a plurality of steps, which may berepeated cyclically to ensure continuous monitoring of environmentalair. One step according to the invented methods is depositing airborneparticles on a regenerative collection surface to form a spot, which maybe accomplished by inertial impaction. Another step comprises measuringa biological signature present in the spot. Examples of biologicalsignatures are provided above. Consequently the presence ofconcentration of airborne biological particles is determined from themeasurement. Where the steps are preformed cyclically, each measurementgenerates a present value of the concentration of airborne biologicalparticles. Values from preceding measurements may be at leasttemporarily stored and used in calculating the average value and thestandard deviation from prior measurements. Thus, a defined number ofprior values can be used calculating the average, for example eight,which are derived from measurements in the preceding cycles. The presentvalue is then compared to the calculated average to determine if thepresent value exceeds the average to a significant extent. The standarddeviation from the prior measurements can be used to establish if thepresent value is abnormally high. Thus, the present value may becompared to the average value plus a preset factor, for example between3 and 8, multiplied by the standard deviation. If the present value doesexceed the average value to a significant extent, then the processoroutputs an alarm signal. Finally, another step is regenerating thecollection surface.

In other aspects, the present invention comprises devices, systems suchas for monitoring and controlling air quality, and networks such ascontrol networks. Different facets of the invention relate toapplications that improve, for example, buildings or public facilities,HVAC systems, airplanes, and generally result in overall safer premises.Sensors based on regenerative surface air samplers can be employed inmonitoring airborne hazards. For example, biological, chemical, orradiological sensors can be set to continuously observe air quality.Sensors based on regenerative surface air samplers may be deployed asstand alone devices, but they may also be incorporated into smart orintelligent sensor networks.

The sensors communicate signals through a communication interface, whichmay be a transmitter in some embodiments. In other embodiments thecommunication interface is a transceiver. Signals are typicallycommunicated over a control network such as a building automation systemnetwork. The communication interface or transceiver can communicatethrough a wired or wireless connection. In some embodiments, thetransceiver communicates via an RF link to an RF link network.

In some embodiments, the sensor based on a regenerative sample mayoutput a positive response that directly activates other devices, forexample specific sensors capable of identification of specific chemical,biological, or radiological species or narrow classes of species,samplers capable of capturing and/or archiving samples of airborneparticles, or other sensors that are not based on regenerative surfaces.

As mentioned above, the sensors preferably communicate to an automationsystem network, such as a LonWorks® automation system or a CEBusautomation system. Preferably, a transceiver communicates through astandard protocol, such as the BACnet protocol or the LonTalk® protocol.

In many embodiments, a controller is communicatively coupled to thesensor. In some embodiments the controller is a Neuron® chip. Typically,the controller is also coupled to the transceiver. In some embodimentsthe controller is coupled to at least one actuator and capable ofactuating at least one air management component in response toinformation received from the sensor. The controller may also becommunicatively coupled to the air management component, and thus it maybe able to receive and integrate information additional to that receivedfrom the sensor. Examples of air management components are air analysisdevices such as sample capture devices, sample analysis devices, orparticle counters, smoke or fire sensors, or air control devices such asair duct dampers.

In another aspect, the present invention relates to methods ofconstructing a sensors network. Accordingly, sensors based on aregenerative surface air sampler can be added into a network. Thesensors may be of biological particles, or chemical or radiologicalsensors. The network may contain any number of additional components,such as smoke or fire sensors.

In yet another aspect the present invention relates to methods ofcontrolling ambient air quality. According to the invented methods,ambient air is sampled with at least one sensor based on a regenerativesurface air sampler. Sampling can take place continuously andautomatically. If at one point sampling by the sensor indicates aprobable threat, a responsive step is performed. The responsive step maycomprise actuating at least one air management component, activating atleast one specific sensor, issuing an alert signal. In case an alertsignal is issued, it may be transmitted to one or several locations,such as facility management or a fire department or law enforcementagency creating a two-tier warning system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of a prior art inertial impactor.

FIG. 2 is a diagram of several components present in various embodimentsof the present invention, namely an impaction plate (205) with acollection surface on which a deposit forms (220), a spotting nozzle(210), an analyzer comprising a fluorescence photosensor (230) and anexcitation light source (240) coupled by wires (250), a shaft (260)mounted to the impaction plate (205) by a bracket (270) and aregenerator (280). Three collection surfaces/spots are drawn only forillustration; a single collection surface suffices in most embodiments.

FIG. 3A and FIG. 3B illustrate two embodiments in which outwardlyprojecting structures are provided on a collection surface to enhanceparticulate collection.

FIG. 4 is a diagram of a method for continuous monitoring of airbornebiological particles.

FIG. 5 illustrates an arrangement of the components of a fluorescencedetector. A UV LED 510 emits an excitatory light 530 that passes throughexcitation filter 520. A dichroic mirror reflects the excitatory UVlight, which then reaches the sample spot 560 on a regenerative surface550. Fluorescent light 580 in the visible part of the spectrum passesthrough the dichroic mirror 540 and an emission filter 570 until itreaches the photodiode detector 590.

FIG. 6 is a flow diagram of the signal processing for determining thepresence unusually high concentrations of airborne biological particles.

FIG. 7 shows transmission profiles of the dichroic mirror, exciter andemitter filters.

FIG. 8 shows results of testing fluorescent aerosol detection using aregenerative collection surface air sampler.

FIG. 9 shows a diagram of a method of controlling ambient air quality.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In one aspect, the invention relates to an apparatus or device forcontinuous monitoring of the concentration and content of airborneparticles. One embodiment is diagramed in FIG. 2. Some components of thedevice are a spotting nozzle, an impaction plate, a detector, and aregenerator. Additional components are present in some embodiments, suchas a virtual impactor and/or a liquid coating applicator.

The spotting nozzle accelerates air from an inlet onto the impactionplate where airborne particles are collected. By spotting nozzle ismeant a jet through which a gas sample is passed and which increases themean velocity of the gas sample to a value sufficient to impart enoughmomentum to particles above a specific size that the particles are ableto impact on an impaction plate as described herein. For example, a gassample may be sucked through a nozzle having a reduced cross-sectionalarea relative to a source of gas using a downstream vacuum pump. Anacceleration nozzle may be of any shape, such as round or slit-shaped. Around acceleration nozzle or jet has a round opening through which gasexits. The nozzle body may be cylindrical. A slit-shaped accelerationnozzle or jet has a rectangular opening, including narrow and nearlysquare-shaped openings, through which gas exits.

Acceptable spotting nozzles have been used in inertial impactors. Anexemplary inertial impactor is shown in FIG. 1. Accordingly, an airsample (1) is drawn through the inlet (2). The sample of air is drawnover the surface of the substrate (3), which collects particles havingan inertia too great to follow the curved path of the air stream. Thesubstrate, or impaction plate, according to the present invention isdescribed below.

An inertial impactor typically refers to a single unit comprising of anair inlet, a spotting or acceleration nozzle, and an impaction plate. Atthe acceleration nozzle exit, the airstreams turns sharply and particleslarger than a certain diameter (referred to as the impactor's cut-offsize) impinge on the collection surface of the impaction plate due toinertial forces. Exemplary inertial impactors are discussed in U.S. Pat.Nos. 6,435,043, 5,553,795, 5,437,198, 4,926,679, 4,796,475, 4,321,822,and 4,133,202.

The physical principles of operation of an inertial impactor is similarto that of a virtual impactor referred to below. A jet of particle-ladenair is deflected abruptly by an impaction plate, which causes an abruptdeflection of the air streamlines. Particles larger than a critical size(the so-called cutpoint of the impactor) cross the air streamlines andare collected on the impaction plate, while particles smaller than thecritical size follow the deflected streamlines. The cutpoint of animpactor is determined by several parameters through the Stokes number.

${St} = \frac{\rho_{p}d_{p}^{2}{UC}_{c}}{9\eta\; D_{j}}$where ρ_(p) is the particle density, d_(p) is the particle diameter, Uis the impactor jet velocity, η is the gas viscosity, and D_(j) is thediameter of the impactor jet (Hinds, “Aerosol Technology”, 1982, JohnWiley & Sons, Inc.). The slip correction factor, C_(c), corrects for thereduced drag on small particles as they approach the mean free path ofthe gas. The collection efficiency for an impactor is oftencharacterized by its D50, the diameter at which 50% of the inputparticles are collected.

The slip correction factor is given by the following equation:

$C_{c} = {1 + {\frac{2}{{Pd}_{p}}\left( {6.32 + 2.01^{{- 0.1095}{Pd}_{p}}} \right)}}$where P is the absolute pressure in Cm Hg and d_(p) is the particlediameter in μm.

The preferred air velocity is greater than 10 m/s and less than 100 m/s,and more preferably greater than 20 m/s and less than 30 m/s. The nozzlediameter is preferably greater than 0.25 mm and less than 2.5 mm, andmore preferably greater than 0.5 mm and less than 1 mm. The nozzle ispreferably located a distance from the impaction surface greater than0.1 mm and less than 2 mm, and more preferably, a distance greater than0.25 mm and less than 0.5 mm.

Inertial impactors and impaction substrates used for collection ofambient particles are known to sometimes exhibit low particle collectionefficiency. Low particle collection efficiency is a result of at leasttwo factors: particles of high momentum impact the substrate and bounceoff, and particles which have been previously collected are displacedfrom the substrate and re-entrained in the airstream (Sehmel, G. A.,Environ. Intern., 4, 107-127 (1980); Wall, S., John, W., Wang, H. C. andCoren, S. L., Areosl. Sci. Technol., 12, 926-946 (1990); John, W.,Fritter, D. N. and Winklmayr, W., J. Aerosol. Sci., 22, 723-736 (1991);John, W. and Sethi, V., Aerosol Sci. Technol., 19, 57-68 (1993)). Inaddition, because these two processes typically depend on particle size,the size distribution of the collected particles can be distorted.

Such problems, however, are not of significant concern for the inventeddevices. Precise knowledge of collection efficiency is not crucial forthe present invention. The only requirement for the collectionefficiency is that it does not vary widely or unpredictably with theconcentration of airborne particles. Thus, under otherwise similaroperating conditions, a larger number of particles should be collectedinto a spot from an air sample with a higher concentration of airborneparticles. A spot is an aggregate of particulates deposited upon asurface in a relatively small area, so that the individually smallparticulates are aggregated together to form a larger spot. Moreover, asdescribed below, the present invention provides for continuousmonitoring of air samples. As a result, it is often detection of changesin the concentration and/or composition of airborne particles in airsamples that is of interest. Detection of such changes is unaffected bya relatively low collection efficiency. Thus, the continuous monitoringfeature of the present invention circumvents some of the shortcomingsusually associated with inertial impactors.

For the same reason, variability of collection efficiency for particleof various sizes does not negatively impact the operation of the presentinvention. In a preferred embodiment, the inertial impactor isconfigured for optimum collection of particles in the 0.5-10 μmdiameter, more preferably in the 1-5 μm range. Airborne particles inthis range are the most likely to represent an inhalation hazards tohumans. Within this range bacteria would be captured, as well aspotentially noxious viruses or protein aggregates. However, the inertialimpactor may be configured for optimal collection of particles of othersize ranges in different applications.

In some embodiments, the intake of the spotting nozzle is downstream ofa virtual impactor. By downstream it is mean that the second component(the spotting nozzle in this case) and the first component (the virtualimpactor) are arranged so that the gas or air sample passes sequentiallythrough the first and then the second component of the system. A virtualimpactor is an apparatus that increases the concentration of airborneparticles of a desirable size range. It separates an airflow into aminor and a major component, wherein the minor component carries amajority of airborne particles above a certain size. Examples of virtualimpactors can be found in U.S. patent application Ser. No. 09/955,481,or in U.S. Pat. Nos. 3,901,798; 4,670,135; 4,767,524; 5,425,802; and5,533,406. Thus, the spotting nozzle can be downstream of the minor flowof a virtual impactor. It is preferable that the virtual impactorincreases the concentration of particles above 1 μm. In someembodiments, more than one virtual impactor is placed upstream of thespotting nozzle. Impacting air with higher concentration of airborneparticles in the desired range increases the collection pace and thusthe efficiency or sensitivity of the invented device.

Additionally, some embodiments contain a size selective inlet forpreconditioning the air sample by removing particles above a desirablesize. A “size-selective inlet” removes particles above a certain size(aerodynamic diameter) from a stream or sample of gas. By “remove” ismeant that at a predetermined particle size, 50% of the particles areremoved from the gas sample and 50% pass through the size selectiveinlet. For particles of smaller sizes than the predetermined size, most,or almost all, particles pass through the inlet, while for particles oflarger sizes, most, or almost all, particles are removed. The substrateof a size-selective inlet collects the removed particles. In certainpreferred embodiments a size selective inlet comprises an inertialimpactor. The size of the particles removed is determined, in part, bythe velocity of the gas sample as it comes out of the accelerationnozzle. The higher the velocity, the smaller the size of the particlesremoved. Thus, by selecting the appropriate acceleration nozzle, apredetermined upper size of particles can be removed from a gas sample.In certain embodiments, a size-selective inlet comprises a filter, anelutriator, or any other device capable of removing particles greaterthan a predetermined size. Preferably, the size selective inlet removesparticles above 10 μm, but may be set to remove particles above othersizes, for example 12 μm, 15 μm, 20 μm, or 25 μm. In those embodimentswhere a virtual impactor is present, the size selective inlet may beplaced either upstream or downstream of the virtual impactor. Removal oflarge airborne particles eliminates potential sources of interferencewith the analyzer discussed below.

The spotting nozzle directs the air stream towards a collection surfaceof an impaction plate, thus depositing airborne particles on thecollection surface of the impaction plate. The collection surfaceaccording to the present invention can be regenerated. Regenerationoccurs by the action of a surface regenerator as described below.Regeneration of the collection surface enables continuous and automaticreuse of the device. Thus, unlike other inertial impactors, the presentinvention does not require a consumable impaction plate.

The impaction plate may take a variety of shapes, but the collectionsurface is typically flat. In some embodiments, the impaction plate is adisk, i.e. flat, thin, and circular. A disk axis is perpendicularly onthe center of the two parallel circular surfaces of the disk. In theseembodiments, the collection surface is on one of the two planar parallelsurfaces of the disk, preferably at some distance from the center of thedisk axis. In other embodiments the impaction plate is a lobed cam. Oneor several substantially planar surfaces are parallel to the cam axisand function as collection surfaces. A cam shaft along the cam axis ispart of the homing sensor as described below.

The impaction plate is preferably made substantially of a homogenousmaterial, although it is possible to embed a collection surface of onematerial on an impaction plate made of a different material. The plate,or at least its collection surface, is made of a material sufficientlydurable to withstand repeated action of the surface regenerator withoutincurring any damage. Many materials are suitable, including glass,quartz, ceramic, silicon wafers metal or plastic. In addition, coatingscan be deposited on one of the above materials to increase the hardnessand/or resistance to abrasion. In a preferred embodiment the plate ismade entirely of UV transparent material, for example fused silica puresilica, or sapphire (Edmond Scientific).

In a preferred embodiment the collection surface is essentially smooth.A smooth surface is preferred as it is easiest to clean by the surfaceregenerator. On the other hand, particles tend to bounce off smoothsurfaces easier, thus decreasing collection efficiency. Consequently, inother embodiments, the collection surface has outwardly projectingstructures, such as rods (FIG. 3A) or ribs (FIG. 3B). For example, thesurface is micromachined to have pyramid-shaped structures ofapproximately 1-10 μm in height and width. In these embodiments,particle loss is minimized, but relatively harsher surface regeneratorsare used.

One function of the impaction plate is to support the collection surfacefor the accumulation of the sample of airborne particles duringimpaction. Accordingly, at one point in the cycle of operation of thedevice, the collection surface is under the spotting nozzle. Typically,the collection surface is horizontal while the spotting nozzle isvertical.

In a preferred embodiment, the impaction plate also functions as part ofthe homing sensor, as discussed below. The spot on the collectionsurface is subject to analysis by the analyzer, and the collectionsurface is regenerated by the surface regenerator (i.e. the surfaceregenerator cleans the spot from the collection surface).

For example, the impaction plate may less than 150 mm in diameter, andmore preferably less than 80 mm in diameter but greater than 20 mm indiamter. The collection surface is preferably less than 25 mm indiameter, and more preferably less than 15 mm but greater than 5 mm indiameter.

Another component of the invented devices is an analyzer forcharactering the content of the spot. Analyzers may take a wide varietyof forms, depending on the type of airborne particles to be monitored indifferent applications. For example, analyzers may detect biologicalparticles, specific chemical compounds, or radioactive particles.Detection may be achieved by any one or combination of availabletechniques, such as mass spectrometry, infrared spectroscopy,fluorescence measurements, or Raman spectroscopy, gamma emission, alphaparticle emission, or beta emissions. Monitoring of biological particlesis described in some detail below. Useful chemical monitoring may be,for example, of nonvolatile toxic chemicals such as VX chemical warfareagent or mercury containing particulate emitted from coal-fired powerplants.

In some embodiments, the invented devices comprise a pre-analysis spotpreparation station. At this point the spot is prepared to enhance itscharacteristics measured by the analyzer. The spot may be combined withcompounds that affect measured properties of the airborne particles ofinterest by squirting a liquid containing the appropriate compound froman inkjet type of device. For example, the liquid may contain matrixsolution used in a Matrix Assisted Laser Desorption Ionization (MALDI)mass spectrometer, or a DNA stain that becomes fluorescent when it isbound with DNA, such as ethidium bromide.

It is preferable that any amount of consumable reagents be kept at aminimum to ensure prolonged maintenance free operation of the devices.In one embodiment, the pre-analysis spot preparation station applies aplasma lysis pulse to the spot to expose the contents of any microbes(see for example U.S. Pat. No. 5,989,824)

Another component of the invented devices is a surface regenerator. Thepurpose of the surface regenerator is to regenerate the surface, i.e. toremove the deposit from the collection surface after analysis, and thusto make the collection surface available for collecting another spot.The surface regenerator must remove substantially all the spot from thecollection surface, so prior use of the collection surface does notinterfere with analysis of subsequently gathered spots.

In some embodiments, especially where a smooth collection surface isused, a surface regenerator may be felt or cloth pad that is pressedagainst a moving collection surface as it slides towards the nozzle. By“felt” is meant a porous fibrous structure, typically unwoven, createdby interlocking fibers using heat, moisture or pressure. Suitable fibersinclude, but are not limited to, polyester, polyurethane, polypropylene,and other synthetic and natural fibers. By “cloth” is meant materialthat is made by weaving, felting, knitting, knotting, or bonding naturalor synthetic fibers or filaments. Of course, movement of a pad relativeto the collection surface while pressed on it may be achieved by manyother known means. Alternatively, a felt or cloth wheel may be used, anda motor spins the wheel when it is in contact with the spot, thusregenerating the collection surface. In other embodiments, the surfaceregenerator is a brush or blade that remove the spot, for example with asweeping motion. When the collection surface is not smooth, one or morebrushes are desirable, and their sweeping motion may be performed inmultiple directions. In yet other embodiments, surface regeneration isachieved by blowing a stream of air at an angle at the spot, i.e. thesurface regenerator comprises a nozzle oriented an angle towards thecollection surface, which blows a stream of air at high velocity towardsthe collection surface. In some embodiments, regeneration is aided byelectrostatically charging the spot either before or during the actionof any regenerator. The collection surface may be temporarily imparted apositive charge, a negative charge, or alternative positive and negativecharges. In some embodiments, the regenerator comprises at least in partheaters or lasers capable of transferring energy to the surfacespot/collection surface. In some embodiments, multiple regenerators arepresent and they are either used sequentially in each cycle of thedevice, or some of them are activated only when necessary, for examplein periodic “deep cleaning” cycles, or in response to sensing incompleteregeneration of the collection surface.

In some embodiments, another component of the invented devices is aliquid coating applicator. The function of the liquid coating applicatoris to spread a droplet of liquid over the collection surface or aportion thereof before impaction of the air sample. The amount of liquidis typically minuscule, and so essentially all of the applied liquidevaporates during the subsequent air impaction with the collectionsurface. The purpose of the liquid is to reduce particle bounce from thecollection surface, at least at the initial stages of gathering thespot. Thus, a spot nucleus forms which reduces particle bounce duringthe remaining time of acquisition of the spot and improving collectionefficiency. In these embodiments, a consumable (the liquid) isnecessary, but it is used up in minute amounts. A relatively smallliquid reservoir thus can contain and make available liquid for a verylarge number of cycles. For example, a 500 ml reservoir might sufficefor 10,000 cycles. Accordingly, replenishing the consumable is requiredquite rarely.

Any liquid capable of trapping impacting particles may be used, such aswater, alcohols such as ethanol or methanol, glycerol, a mineral oil, ormedium weight hydrocarbons such as octane. It is important that theliquid does not affect the collected spot so as to interfere with itssubsequent analysis.

The amount of liquid necessary may vary with the nature of the liquidand other features and dimensions of the device. Usually, the volume ofliquid for each application is from 0.5 μl to 50 μl, and may be, forexample, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45,or 50 μl. It is preferred that an identical volume of liquid is appliedin each cycle of operation.

Any device capable of spreading a liquid droplet on a surface may beused as an applicator in the present invention. In a preferredembodiment, the applicator is a felt tip pen.

Another component of the invented devices is a homing sensor. Thefunction of the homing sensor is to move the collection surface betweenthe spotting nozzle, the analyzer, the regenerator, and, in someembodiments, the liquid coating applicator. Thus, each component of theinvented device can perform their respective function on the collectionsurface.

The homing sensor is a mechanical device that alters the position of thecollection surface with respect to the other components. Thus, thehoming sensor is not a sensor in the usual meaning of the term, althoughin some embodiments one or more sensors may be present and capable todetect and communicate the position of the collection surface within thefunctional cycle. Many types of mechanisms can be used as homingsensors. In one embodiment, the spotting nozzle, analyzer, regenerator,and liquid coating applicator if present, have fixed positions. Thecollection surface is on a face of a disk. On the opposite face a shaftis attached down the axis of the disk, the shaft being coupled to aprime mover. The disk can thus be rotated at predetermined angles toposition the collection surface sequentially for each component. Inanother embodiment, the impaction plate is a lobed cam having a shaft.There is at least one planar collection surface essentially parallel tothe shaft. In these embodiments, the homing sensor comprises theimpaction plate, shaft and prime mover. Those of skill in the art willrecognize that other mechanical structures can accomplish the functionof the homing sensor. Thus, the collection surface may be movedsubstantially linearly, or the collection surface may be retained in afixed location while other components are repositioned with respect tothe collection surface. Accordingly, any known means of translocationgthe collection surface relative to other components may be used.

In operation, an air stream is pulled through the air inlet of thespotting nozzle. The air stream is a sample of environmental air. Thesample is pre-concentrated in some embodiments by the action of avirtual impactor upstream of the air inlet of the spotting nozzle, sothat the air stream is enriched in particles of the 1-10 μm range. Theair sample is also preconditioned in some embodiments by the action of asize selective inlet upstream of the spotting nozzle to eliminateparticles above a desired size, such as 10 μm, to improve the desiredair composition.

The air stream emerging from the spotting nozzle impacts on thecollection surface of the impaction plate. As a result, a spot formsthat consists mainly of particles in the desired size range, which ispreferably of an aerodynamic diameter of 1-10 μm. The collectionefficiency of the collection surface may be low as long as it is roughlyconsistent for different particle concentrations. By collectionefficiency is meant the proportion of particles in the desired sizerange in the air sample that is trapped on the collection surface as aresult of impaction.

In some embodiments, prior to impaction of the air stream by thespotting nozzle, the collection surface of the impaction plate is coatedwith a liquid by the action of a liquid coating applicator. The liquidcoating improves the collection efficiency of the collection surface.

The position of the collection surface relative to other components ofthe invented devices changes through the action of a homing sensor.Thus, the homing sensor automatically positions the collection surfacesequentially from the liquid coating applicator, if one is present, tothe spotting nozzle, to the analyzer, and to the regenerator orregenerators. In some embodiments, the homing sensor may be able to varythe order of repositioning the collection surface in certaincircumstances. For example, the homing sensor could be able to move thecollection surface from the regenerator to the analyzer if or when it isdesirable to ensure proper regeneration of the collection surface.

After a spot accumulates on the collection surface by the action of thespotting nozzle, movement of air through the spotting nozzle usuallyceases and the collection surface with the spot moves to the analyzer.In some embodiments, a first step at this stage is preparing the samplefor analysis at the pre-analysis spot preparation station. The analyzerthen detects the presence and/or measures the concentration specificairborne particles or constituents thereof.

Following analysis, the collection surface is moved by the homing sensorto the surface regenerator, which acts to clean the collection surfaceand thus regenerate it for another cycle of operation. The regeneratormay act by one or several mechanisms to regenerate the collectionsurface. Thus, the regenerator could act by a mechanical brushing orwiping of the surface, by blowing an air stream at high velocity towardsthe spot, preferably at an angle, and/or by electrostatically chargingthe spot. Following the action of the regenerator, the collectionsurface is used again in another cycle of collection, analysis, andregeneration. The number of cycles that a device can performautomatically without any need for service is very large, preferably inthe thousands.

In another aspect, the present invention relates to methods forcontinuously monitoring airborne particles (see FIG. 4). The airborneparticles being monitored are preferably biological particles, althoughspecific chemicals or radioisotopes may also be monitored, andmonitoring implies detection of their presence, their concentrationand/or possibly their nature. Continuous detection refers to repeatedsampling of environmental air. By continuous it is not meant thatnecessarily air samples are uninterruptedly being evaluated, but ratherair samples may be evaluated at repeated time intervals. Thus, detectionof airborne particles occurs in cycles that comprise at least someidentical steps. The main steps of each cycle are immobilizing airborneparticles on a collection surface, analyzing the immobilized airborneparticles, and regenerating the collection surface. Additional steps areperformed in some embodiments.

A step according to the present methods is depositing airborne particleson a collection surface (440). At this step, airborne particles areextracted from ambient air. Any known extraction methods may be used ifit results in depositing airborne particles on a collection surface. Ina preferred embodiment, however, depositing airborne particles isachieved by inertial impaction.

As a result of depositing airborne particles, a spot forms on thecollection surface. The spot contains extracted or immobilized airborneparticles from the ambient air sample. However, not every particle inthe original ambient air sample needs to be deposited on the collectionsurface at this step. It is envisioned that particles of a desirablesize range may be enriched in the spot. In fact, in some embodimentsparticles of undesirable size ranges may be actively excluded. Theprecise size range differs as required by specific applications. Inpreferred embodiments, particles of 1-10 μm comprise the desirable sizerange. Particles in this size range may be inhaled and may includedangerous biologicals.

In some embodiments, airborne particles of a desirable size range areconcentrated in a step preceding depositing airborne particles on thecollection surface (420). Concentration may be achieved, for example, bythe action of a virtual impactor. This concentration of particles allowsquick sampling of large volumes of air, which decreases the timerequired for performing each cycle of the invented methods, andtherefore improves the performance and ultimately the safety of the air.

In some embodiments the sampled air is preconditioned prior todepositing airborne particles on the collection surface (410). Bypreconditioned it is meant that particles greater than a desirable sizeare removed from the sample. This may be accomplished with a sizeselective inlet as discussed above. Particles greater than the desiredsize range may be first removed from the air, and thus such particles donot end up in the spot. Consequently, they cannot interfere with theanalysis of the spot described below. Preconditioning may remove, forexample, particles greater than 10 μm, but may remove only particlesgreater than other sizes, for example 5 μm, 7 μm, 8 μm, 12 μm, 15 μm, 20μm, or 25 μm. In some embodiments, both preconditioning andconcentration are performed prior to depositing particles on thesurface.

In some embodiments, another step that may be performed prior todepositing airborne particles is moistening the collection surface(430). Many types of liquids may be used to moisten the collectionsurface including glycerol, alcohols, or medium weight hydrocarbons,such as octane, as mentioned above in describing the liquid coatingapplicator. The precise volume of liquid used in each cycle depends onseveral different variables, and may be about 0.5, 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 15, 20, 25, 30, 35, 40, 45, or 50 μl.

Another step of the invented methods comprises analysis of the spot(450). The type of analysis performed depends on the nature of theparticles to be monitored. Appropriate analyses of spots for biologicalmaterials are described in some detail below. Chemical, radiological, orany other type of analysis may be performed according to any knownsuitable test. In some embodiments, analyzing comprises an optional stepof pre-treating the spot so as to enhance the measured signal. Thus,pre-treating may comprise adding to the spot a liquid comprising ananalysis-enhancing compound. In some embodiments where analyzing isaccomplished by MALDI mass spectrometry, pre-treating may be performedby plasma lysing.

Another step of the invented methods comprises regenerating thecollection surface (460). The precise nature of the physical act thataccomplishes regeneration depends on many variables such as theapplication that employs the methods, the expected average aircharacteristics, or the type of collection surface used. Regenerationmay be achieved by any one or combination of steps. For example, in someembodiments, regeneration is accomplished by pressing a felt pad againstthe collection surface and moving the felt pad over the collectionsurface. In other embodiments a felt wheel is rotated while pressedagainst the collection surface. In other embodiments the collectionsurface is electrostatically charged as part of the regeneration step.In other embodiments regeneration is accomplished by brushing thecollection surface with a brush. In other embodiments regeneration isaccomplished by blowing an air jet at high velocity towards thecollection surface. In other embodiments, regeneration is accomplishedby scraping or wiping the collection surface with a blade. Regeneratingthe surface may be achieved by one or more acts. When more than one actis used, the acts may be similar or identical, or they may be different.In some embodiments, specific regeneration acts are not necessarilyperformed in each cycle.

In some embodiments all the cycles of the invented methods areidentical. In other embodiments, some cycles may comprise differentsteps from other cycles.

In some embodiments, the invented methods in at least a subset of cyclescomprise verifying the regeneration of the surface (470). Accordingly,the collection surface is analyzed again after regeneration. Thisanalysis may be performed essentially by the same process or test thatwas used for analyzing the spot. Thus a background signal level isobtained for the regenerated surface. The background signal level isthen compared to predetermined criteria. If the background level isfound to be higher than desirable, regeneration and verification isrepeated until the background signal level meets predetermined criteria.Alternatively, a test may be employed in assessing if regeneration wasacceptably accomplished that is different from the sample analysis test.

Each cycle of the invented methods may be considered to start withdepositing airborne particles on the collection surface to form the spot(440). In those embodiments that comprise preconditioning (410) and/orconcentrating (420) the air sample from which particles are extracted,the additional step(s) can occur essentially simultaneously with thestep of depositing particles on the surface. In those embodiments wherethe methods comprise moistening the collection surface (430), this stepmay be seen as the first step of each cycle. Of course, given thecyclical nature of the invented methods, the selection of any step asthe first is arbitrary.

After completion of the depositing step, each cycle comprises the stepof analyzing the spot present on the collection surface (450). Duringanalysis, data regarding properties of the sample is gathered andtransmitted. This way, the methods are useful in acquiring and conveyinginformation about the presence and quantity of airborne particles ofinterest such as biological particles.

After analysis the next step is regenerating the collection surface(460). The surface is regenerated by any one or more feasible means. Insome embodiments, proper regeneration is verified in at least a subsetof cycles (470). Thus, the collection surface may be re-analyzed.

After regeneration, the next cycle proceeds with depositing airborneparticles from another air sample, which is preceded in some embodimentsby moistening the collection surface.

In another aspect, the present invention relates generally to devicesuseful for monitoring airborne biological particles. The devices cananalyze the content of extracted particles deposited as a spot on acollection surface, preferably a regenerative. By regenerativecollection surface it is meant a collection surface on which a spot ofairborne particles can be deposited or immobilized for a period of time,and then the spot can be removed thus regenerating or refreshing thesurface. The regenerated collection surface has similar characteristicsto the collection surface prior to the previous spot immobilization. Thesurface refreshing need not necessarily achieve virtually identicalcharacteristics. Rather, the surface must be sufficiently regeneratedthat the next signal resulting from any residue will be insignificantrelative to the signal resulting by the sample spot. Thus, theregenerative collection surface can be used in numerous similar cyclesof spot immobilization and regeneration. Regenerative collectionsurfaces are described in more detail above.

The devices also comprise in some embodiments the means of extractingparticles from ambient air and depositing or immobilizing them on thesurface, such as an inertial impactor. Thus, the airborne particles areimmobilized on a collection surface as a spot.

The invented devices comprise a detector that is capable of analyzingthe content of the spot. The detector determines the presence of aproperty inherent to biological particles, thus determining the presenceand/or concentration of airborne biological materials, which may includebiohazards. Biological materials may be bacteria and/or viral and/orprotein aggregates. As bacteria can clump together, the term “particle”as used herein is understood to include inert particles, a singlebiological entity or biological (typically 0.5-2 μm), or an aggregate ofthese small biologicals (aggregates of about 2-10 μm).

Any known property inherent to biological particles or to specificsubsets of biological particles may be subject to analysis. There aremany examples of such properties, sometimes called biologicalsignatures, and they may be detected by optical or non-optical methods.Examples of known useful properties include fluorescence that may becharacterized by single or multi-wavelength excitation and/or emissionand/or fluorescence lifetime, IR absorption, Raman scattering, massspecters, or terahertz specters. Examples of useful analyticaltechniques include fluorescence spectroscopy, Fourier-transform infraredspectroscopy, laser induced breakdown spectroscopy or aerosoltime-of-flight mass spectrometry, MALDI mass spectrometry, surfaceenhanced Raman spectroscopy, planar optical waveguide sensing byevanescent waves, or terahertz spectroscopy.

During analysis, the spot produces a signal that is measured by anysuitable detection means. Where the signal is detected optically,detection may be accomplished using any optical detector that iscompatible with the spectroscopic properties of the produced signal. Theassay may involve an increase in an optical signal or a decrease. Theoptical signal may be based on any of a variety of optical principles,including fluorescence, elastic scattering, light absorbance,polarization, circular dichroism, optical rotation, Raman scattering,and light scattering. Preferably, the optical signal is based on theintrinsic fluorescence of biological particles.

In general, the optical signal to be detected will involve absorbance oremission of light having a wavelength between about 180 nm (ultraviolet)and about 50 μm (far infrared). More typically, the wavelength isbetween about 200 nm (ultraviolet) and about 800 nm (near infrared). Avariety of detection apparatus for measuring light having suchwavelengths are known in the art, and will typically involve the use oflight filters, photomultipliers, diode-based detectors, and/orcharge-coupled detectors (CCD), for example. The optical signal producedby a spot may be based on detection of light having one or more selectedwavelengths with defined band-widths (e.g., 500 nm+/−0.5 nm).Alternatively, the optical signal may be based on the shape or profileof emitted or absorbed light in a selected wavelength range. Thisprofile can measured by an array of narrow bandwidth sensors or with aspectral photometer (such as that sold by Ocean Optics, Inc.) Thesignals may be recorded with the aid of a computer.

In preferred embodiments the analyzer is a fluorescence detector, whichcomprises an excitation light. source for stimulating the fluorophoreson the collection surface and a fluorescence photosensor for measuringthe resulting emissions from the spot. The optical signals produced byindividual spots may be measured sequentially by iterativelyinterrogating the deposit with light of different wavelengths and/ormeasuring different emission characteristics.

In some embodiments, the optical signal measurement will involve lighthaving at least two distinctive wavelengths in order to include aninternal control. For example, a first wavelength is used to determinethe presence or concentration of biological materials, and a secondwavelength is used to determine the presence or concentration ofnon-biological materials that may interfere with the reading at thefirst wavelength. An aberration or absence of the signal for the secondwavelength is an indication that the sample was improperly prepared, theestimate of concentration of biological particles is unreliable in thatcycle, nonbiological airborne materials are present and affect thefluorescence expected from biological particles in the sample, or theanalyzer is malfunctioning.

Biological materials are known to contain autofluorescent materials. Forexample, fluorophores include the aromatic amino acids tryptophan,tyrosine, and phnylalanine, nicotinamide adenine dinucleotide compounds(NADH and NADPH), flavins, and chlorophylls. In addition, culturedbacteria are known to have characteristic fluorescence featuresdistinguishable from wild bacteria. This property may be employed in thedesign of the biological alarm as biological weapons are typicallyproduced in cultures.

In some embodiments, improved discrimination between biologicalparticles and other non-biological particles is possible byincorporating several excitation wavelengths in sequential manner,thereby interrogating each sample spot multiples times.

Measuring intrinsic fluorescence of particles trapped in a spot requirescomparatively less sophisticated equipment than that necessary forsimilar measurements of particles in an airborne state. Fluorescenceemissions are typically higher due to the presence of concentratedfluorophores. Excitation can thus be performed with less powerfulsources, for example, depending on the embodiment with typicalelectric-arc lamp, LED or laser diodes, although any other types oflasers may also be used. For example, laser diodes or LEDs suitable forsome embodiments may be obtained from Nichia Corporation, Tokushima,JAPAN. In addition, excitation for longer time periods is possible. Insome embodiments, fluorescence spectra can be collected, while in othersonly peak fluorescence emission is of interest. Additionally, severalautofluorescence characteristics can be determined for each spot. Forexample, as detailed below, fluorescence emitted in response toexcitation at about 266 nm, 340 nm, 360 nm and/or 400 nm, may bemeasured for each spot.

Fluorescence detectors comprise an excitation light source, such as anUV light source, and a fluorescence photosensor for measuring lightemitted from a sample in response to excitation. Any light detector canbe used as a detection device. Three common detectors are (1)photomultiplier tubes (PMT), (2) avalanche photo-diodes; and (3)solid-state silicon photo diodes. Focusing the light may be importantdepending on the type of detector that is used. For example, avalanchephoto-diodes have relatively small detection surfaces. Consequently,when using avalanche photo-diodes, it is preferable to focus the lightso as to direct the light to the avalanche photo-diode's detectionsurface. Focusing the fluorescence signal to a small sensor ispreferable because it will becomes more likely for stray light to missthe sensor. In some cases, smaller sensors have less noise than sensorswith larger active areas.

In one embodiment the excitation light source is positioned underneath ahorizontal UV transparent impact plate, and the emission sensor ispositioned above the plate, as is the collection surface (see FIG. 2).For example, the impaction plate may be shaped as a disk or mayotherwise be planar. Accordingly, the impaction plate has a collectionsurface side, on which the spot forms, and a side opposite to thecollection surface side, which may be called the interrogation side. Insome embodiments, the impaction plate is made at least in part of amaterial substantially transparent to ultraviolet radiation. In theseembodiments the spot is collected on a UV transparent collectionsurface. In these embodiments, the impaction plate allows components ofUV-based detectors, such as an excitation light source and fluorescencephotodetector, to be placed on the two opposite sides of the impactionplate. Thus, the excitation light source may be placed on theinterrogation side and the fluorescence photosensor is placed on thecollection surface side.

In other embodiments, the excitation light source and the photosensorare both placed on the same side. The fluorescence is separated from theexcitation light with optical filters. One example of such an embodimentis illustrated in FIG. 5. An UV LED (510) emits light (530) of anexcitatory wavelength, which may be in the range of about 340 to 380 nm.The excitatory radiation is reflected by a dichroic mirror (540) towardsthe spot (560) deposited on a collection surface. The dichroic mirrorsubstantially reflects excitatory radiation and is substantiallytransparent to fluorescence radiation, in this case in the visible partof the spectrum (see FIG. 7 for the transmission characteristics of thedichroic mirror, excitation and emission filters). Fluorescenceemissions (580) pass through the dichroic mirror (540) and an emissionfilter (570), then reaching the photodiode (590). Focusing lenses arenot shown in the drawing.

Those of skill in the art appreciate that many variables can beoptimized, for example angles between the emitter and sensor may beadjusted for maximum signal to noise ratio, filters may be used toreduce or eliminate undesirable wavelengths, or an excitation laser beammay be pulsed and the receiver coupled to the photodetector may be gatedto respond in a delayed manner during a short period following eachlaser illumination pulse, so as to discriminate against false ambientillumination.

The spot is immobilized for an amount of time suitable for multipleanalytical measurements. Thus, the intrinsic fluorescence properties ofthe deposit may be analyzed sequentially at different excitationwavelengths. For example, excitation wavelengths may be of about 266 nm,340 nm, and/or 400 nm. Excitation at different wavelengths is desirablein some embodiments, as it is expected that non-biological materialsalso autofluoresce thus interfering with accurate quantification ofbiological materials present in the spot. Furthermore, it may bepossible to distinguish between various classes of biologicals bymeasuring the fluorescence signature and comparing that signature toknown signatures for specific classes of biologicals. For example, byusing multiple wavelengths of excitation light and measuring thefluorescence emission spectra over at least several ranges ofwavelengths, it may be possible to differentiate bacteria, viruses,bacterial spores, mold spores, and fungi. Within each class, it may bepossible to identify cultured from naturally occurring specimens. Thus,a better characterization of biological materials is possible throughcharacterization of fluorescence of airborne particles in response todifferent excitation wavelengths.

In another embodiment, a particle counter may be used in parallel with asensor based on a regenerative surface to assist in the characterizationof the biologicals. Particle counters use light scattering as particlespass through a beam of light to measure the density particles in air.Some particle counters are also capable of determining the size of eachparticle. Some particle counters are capable of assessingcharacteristics of the particle shape based on the particle's lightscattering properties. If a particle counter is capable of measuringeither or both the size and the shape of many particles in a shortperiod of time, then a dynamic measure of either or both of the particlesize distribution and particle shape distribution in air coincident withthe particles being analyzed by the sensor based on a regenerativesurface. Thus, a better characterization of biological materials ispossible through characterization of fluorescence, combined withparticle counts broken down by either or both of size and shape.

In another embodiment, two detection methods can be used in sequentialcombination within a sensor based regenerative surface air sampler toassist in the characterization of the biologicals. For example, afterthe sample spot is created, the spot may be analyzed sequentially byfluorescence and then by Raman. A Raman sensor may be capable todifferentiate various species or genii within a specific class ofmicrobes. Such a combination of sensors would allow for greaterconfidence in the need to indicate an alarm in response to a particularsample spot.

One useful excitation wavelength is 266 nm, which excites amino acidstryptophan and tyrosine, which have peak emissions around 340 nm and 310nm respectively. 266 nm UV light also excites NADH and riboflavin, whichhave emission peaks from airborne particles around 450 nm and 560 nmrespectively. In addition to 266 nm, it is feasible to use other closewavelengths, for example 220, 225, 230, 235, 240, 245, 250, 255, 260,265, 270, 275, 280, 285, 290, or 295 nm. While nonbiological airborneparticles within the size range of interest also fluoresce in responseto 266 nm UV light, the fluorescence spectra of tryptophan andtyrosine-containing particles exhibit characteristic intensity peaks(between about 310-350 nm; see Pan et al., Field Analytical Chemistryand Technology 3:221-239, 1999). These characteristic peaks can be usedto quantitatively distinguish the amount of biological materialsrelative to non-biological particles which typically have broademissions spectra. For example, emissions at the expected peak intensityof about 340 may be normalized to emissions at other spectral regions,for example around about 400 nm and/or 500 nm.

Another useful excitation wavelength is about 340 nm. Two relatedfluorescent coenzymes or biomolecules are found in all living cells:nicotinamide adenine dinucleotide phosphate (NADP) and nicotinamideadenine dinucleotide (NAD). They are essential for cellular metabolism,and therefore their fluorescence can serve to monitor the presenceand/or concentration of airborne bacteria. In other words, thesemeasurements are especially suitable for determining the presence and/orconcentration of viable airborne cells, such as bacterial cells. Thefluorescence excitation and emission wavelengths of NADH are wellseparated, which facilitates detection. The excitation wavelength ofNADH/NAD(P)H is centered at 340 nm in the near ultraviolet spectrum, andtheir fluorescent emission wavelength extends from 400 to 540 nm. Thus,a desirable excitation wavelength is about 340 nm, but it is feasible touse other close wavelengths, for example 320, 325, 330, 335, 345, 350,351, 355, 360, 370, 375, or 380 nm.

Riboflavin, a flavonoid, has fluorescent wavebands that partiallyoverlap those of NADH, so it may also be detected by a system designedfor NADH, or it may be detected in separate measurements. Riboflavin,exhibits peak excitation at approximately 400 nm, with characteristicemission between 475 nm and 580 nm (Li et al. in Monitoring CellConcentration and Activity by Multiple Excitation Fluorometry,Biotechnol. Prog., 1991, p: 21-27). The presence of both NADH andriboflavin are characteristic of viable bacteria in an air medium. Thus,autofluorescence in response to these wavelengths of excitation canindicate the presence of viable bacteria or cells (see, for example,U.S. Pat. No. 5,895,922, and U.S. patent application Ser. No.09/993,448). The longer excitation wavelength of less energy also makesit less likely for fluorescence to occur in a wide group ofnon-biological particles that would interfere with the measurements.

As mentioned above, the detector produces signals, typically electricalsignals, which are related to the biological signature detected. Thesignals are conveyed to a receiver, which may then relay the signals forfurther processing. The signals typically reach a processor, which maybe a computer or a Neuron Chip® as described in more detail below. Theprocessor is capable to process or interpret the signals and thusestablish or gauge the concentration of biological particles in thespot. Such signal processing may be performed according to the methodsoutlined below. Consequently, the processor is capable to establish whenthe concentration of biological particles in the spot exceeds apredetermined value. In such a case, the processor outputs an alarmsignal that alerts users of the presence of potentially harmful airbornebiological particles.

In one embodiment, a photodetector is connected to current-to-voltageconverter if the photodetector outputs a current proportional to theincident light. This voltage may need amplification to give an outputsignal in the 0-5 volt range. The signal may require filtration toreduce the noise, thereby increasing the signal to noise ratio. Thesignal is then fed to an analog-to-digital converter. The digital signalis then read and processed by a microprocessor.

In yet another aspect, the present invention relates to methods ofdetecting specific airborne particles or monitoring concentrations ofairborne biological materials. The methods comprise a plurality ofsteps, which may be repeated cyclically to ensure continuous monitoringof environmental air.

One step according to the invented methods is depositing airborneparticles on a regenerative collection surface to form a spot, which maybe accomplished by inertial impaction.

Another step comprises measuring a biological signature present in thespot (FIG. 6). Any biological signature and its correspondingmeasurement known in the art, including those discussed in some detailabove, may be utilized at this step. Consequently this measurementindicates the concentration of airborne biological particles. Eachmeasurement performed on a spot deposited on a regenerative surfaceprovides a value of the concentration of airborne biological particles(610).

Values from a defined number of preceding measurements may be storedtemporarily. They can be used in calculating the average value and thestandard deviation from prior measurements. Any number of measurements,for example 3, 4, 5, 6, 7, 8, 9, 10 or more, may be used in calculatingthe average and standard deviation. The number of preceding measurements(n) used in calculations is typically constant.

The value of the last measurement is then compared to the calculatedaverage of preceding measurements to determine if the present valueexceeds the average to a significant extent (620). The standarddeviation from the prior measurements can be used to establish if thepresent value is abnormally high, i.e. if the present value exceeds theaverage to a significant extent. Thus, the present value may be comparedto the average value plus a preset number (p) multiplied by the standarddeviation (630). For example, the preset number may be between 2 and 8,although it may be set at different levels depending on specificoperating conditions of the invented methods. If the present value doesexceed the average value to a significant extent, then the processoroutputs an alarm signal (640). Other algorithms may also be suitable andby be preferable for specific applications.

Another step is regenerating the collection surface. Then, the processorproceeds to analyze a newly obtained present value from another spot.

In other aspects, the present invention provides sensors, sensor systemsand networks based on regenerative surface air samplers. Integrated invarious applications, the invented devices and systems are useful formonitoring and controlling air quality, as well as warning promptly ofthe presence of potentially noxious airborne hazards. Sensors based onregenerative surface air samplers can be adapted to monitor the presenceof any airborne hazard. For example, biological, chemical, orradiological sensors can be used to continuously detect the presence ofrespective particles in the ambient air.

By sensors it is meant devices that are responsive to changes in thequantity to be measured. As used herein sensors may encompasstransducers that convert measurements into electrical signals.

Sensors according to the present invention are desirable in a largenumber of civilian or military contexts. They are especially useful indensely populated and possibly closed areas. For example, they aredesirable in buildings or public facilities like stadiums or auditoriumswhere a large number of people may get simultaneously exposed toairborne hazards. They may be mounted on walls or ceilings, and may beespecially useful in air ducts and air plenums, at entrance or deliverypoints. As such, sensors may interact with HVAC systems, or may be partof HVAC systems. The present sensors may also be useful in any vehiclessuch as airplanes or cruise ships.

Sensors based on regenerative surface air samplers may be embodied asvarious types of devices. As those of skill in the art will appreciate,devices attached to sensors may have various types of processingcapabilities. Dumb sensors may simply generate analog or digitaluncalibrated or calibrated outputs. Smart sensors may fuse or correlatedifferent readings to send a number of different types of alerts, orhave communication capabilities and can be programmed to send raw dataand/or sets of alerts. Intelligent sensors can additionally reason abouthow to investigate and resolve their own alerts. The sensors communicatetheir signals through a communication interface. In simpler embodiments,the sensors may merely issue a local audio or visual signal. In otherembodiments, however, the sensors communicate information through thecommunication interface to one or more distant locations. Thecommunication interface may be simply a transmitter in some cases, suchas with dumb sensors. In other embodiments the communication interfaceis a transceiver, i.e. a device that is both a transmitter and areceiver for a communications channel.

Signals from and to sensors may be communicated by any known feasiblemeans. As such, signals are communicated through wired or wirelessconnections. Examples of wired connections include twisted pair,coaxial, power lines, or fiber optic cables. Examples of wirelessconnections include radio frequency (RF), infrared (IR) communicationmeans. For example, in some embodiments the transceiver communicates viaan RF link to an RF link network.

In many embodiments a controller is coupled to the sensor. In someembodiments, the controller is a programmed personal computer or othercomputer with processor, memory and I/O devices. In some embodiments thecontroller is a Neuron® chip, a system-on-chip microcontroller used withLonTalk®, LonWorks® communications protocol referred to below. Differentchip versions share the same basic features in various combinations:processor cores, memory, communications, and I/O, as well as sensors,actuators, and transceivers. The Neuron® chip is actually three, 8-bitinline processors in one. Two of the processors execute the LONWORKSprotocol referred to below, and the third is for the device'sapplication. The chip is, therefore, both a network communicationsprocessor and an application processor. Typically, the controller isalso coupled to a transceiver. In some embodiments, the function of thecontroller may be performed by more than one computer or controller,which may be coupled through a network. The controller may incorporatesoftware or firmware used to operate sensors based on regenerativesurfaces. The methods of operation embodied in the software or firmwaremay be substantially similar to the methods of detecting biologicalparticles disclosed herein. The controller may operate or integrateinformation from other system components as described below.

Signals from the communication interface are typically communicated overa network or system that may be a computer data network, but is moretypically a control network, such as a building automation network.There are many examples of systems in which sensors based onregenerative surface air samplers may be integrated. One such system isthe CEBus system, which has been made an EIA standard, known as the EIA600 standard, which was originally developed by Intellon Corp. A secondsystem is the LonWorks system commercially available from and developedby Echelon Corp, San Jose, Calif. Both the CEBus and LonWorks systemsspecify physical and link layer means for communicating over a varietyof different media including power line, coaxial cable, fiber opticcable, radio frequency (RF), infrared (IR) and twisted pair cable. Whilethe sensors may be adapted to communicate by a variety of means, it ispreferable that the sensors communicate to a local operating networkusing a standard protocol, such as the BACnet (ISO standard 16484-5)protocol or the LonTalk® (also known as the ANSI/EIA 709.1 ControlNetworking Standard) protocol, CEBus, X10 or CAN. Sensors based onregenerative surfaces may also be integrated into any other sensornetwork, such as the one described in U.S. patent application Ser. No.10/021,898.

In some embodiments the controller is coupled to at least one actuatorand configured to operate at least one air management component inresponse to information received from the sensor. Thus, in response to apotential hazard indicated by the sensor, the controller may turn on oneor more components. It may be useful to activate different types ofsystem components in such situations. The components may be looselycategorized as air analysis devices, air control devices, orself-diagnostic devices. Depending on the configuration of the system,the actuated devices may be near or far from the sensor that issued theoriginal alert, and they may be located indoors or outdoors. Thecontroller may also be communicatively coupled to the air managementcomponent, and thus it may be able to receive and integrate informationadditional to that received from sensors based on regenerative surfaces.Evacuation alarms may be triggered based solely on information from asensor based on a regenerative surface, or may be triggered based onadditional information also available.

Air analysis devices may be any devices known in the art that would beuseful in analyzing the composition of air. Examples of suitable devicesinclude a light detection and ranging (Lidar) system, an aerodynamicparticle sizer, a mass spectrometer to detect chemicals present in thethreat, sample capture and archival devices (as in U.S. patentapplication Ser. No. 10/366,595) or specific antibody or PCR basedsensing to precisely identify agents in the threat. Use of specificsensors may minimize the impact of false alarms. They also provideinformation valuable for treatment of affected personnel. Sensors ofthis type perform DNA analysis using the PCR technology, and antibodyanalysis using antibody-based assays.

Air control devices control the flow of air, such as by operatingdampers of an HVAC system. Thus an HVAC system can be used to controlthe flow of air within a building in response to a threat. If the threatis exterior to the building, air is stopped from entering the building,or air is taken in through alternate air intakes that do not appear tobe affected by the threat. If the threat is from within the building,its location can be identified, and air exhausted from the threatenedarea, while providing fresh, unaffected air to the non affected areas ofthe building. Other examples of air control devices include UV lights,heat or microwave, HEPA filters, and corona based disinfection, chemicalfoggers, thermo or photocatalytic filters, or carbon filters.

In some embodiments, sensors based on regenerative surfaces haveself-diagnostic capabilities. Operation of various components theregenerative surface sensor may be itself monitored by one or moresensors, which may be coupled to the controller. The controller may turnon a self-diagnostic program either periodically or as part of aresponse to an alarm by the sensor.

Because sensors based on regenerative surfaces are desirably active inemergency situations, in some embodiments they include a battery backup.Thus, while the sensors are routinely powered from a regular alternativecurrent outlet, they may have a battery backup to be used during poweroutages.

Data on the control network may be transmitted or accessible to a largenumber of interested persons, or organizations, or systems, such asfacility managers, fire departments or law enforcement agencies, and/orbuilding security systems.

In operation, sensors based on regenerative surfaces operate virtuallycontinuously in a sampling mode. When they detect a high probability ofpresence of airborne hazards, they issue an alert signal, which may becommunicated locally and/or remotely. At the same time, depending on thespecific embodiment, the sensors may activate a self-diagnosis program,activate specific sensors, and/or initiate prophylactic measures such asoperate air duct dampers to contain the contamination, or increaseintake of outside air by the HVAC system.

System components other than sensors based on regenerative surfacesusually operate in a standby mode to conserve power and reagents. Theyare controlled based on input detection by sensors based on regenerativesurfaces and/or other early detection sensors, and are placed in anactive mode only when a potential threat is detected. The networkprovides the ability to tailor sets of sensors based on an area to beprotected in combination with different threat scenarios. In the case ofa building or other enclosed structure, both large and small releases,as well as slow and fast releases, of agents may occur either internalor external to the structure. The rate of release is also variable. Bycorrect placement of the sensors, each of these scenarios is quicklydetected, and appropriate measures may be taken to minimize damage fromthe threat. The network may provide input to a heating and ventilationsystem, or the security management system of the structure in a furtherembodiment to automate the control response.

In another aspect, the present invention relates to methods ofconstructing a sensors network. Accordingly, sensors based on aregenerative surface air sampler can be added into a network. Thesensors may be of biological particles, or may be of other types such aschemical or radiological sensors.

In yet another aspect the present invention relates to methods ofcontrolling ambient air quality and alerting those potentially affectedby airborne hazards (see FIG. 9). According to the invented methods,ambient air is routinely monitored with at least one sensor based on aregenerative surface air sampler in a continuous sampling mode (910).Sampling can take place continuously and automatically for extendedperiods of time. As long as no potential hazard is detected (920)continuous sampling (910) is performed. If at one time sampling by thesensor indicates a probable threat (920), at least one responsive actionis taken performed (930). For example, the responsive step may compriseactuating at least one air management component (940), such asactivating at least one specific sensor. A warning signal (950) may alsoissued immediately upon initial detection of the hazard or afterconfirmation of the presence of a hazard at a second location. In casean alert signal is issued, it may be transmitted to one or severallocations, such as building controller, facility management, and or afire department or law enforcement agency.

The invention provides several advantages compared to current relatedtechnologies, although all advantages are not necessarily present inevery embodiment of the invention. Unlike most extractive techniques,the disclosed invention is automatic and requires little or noconsumable items. Consequently, it requires human intervention quiterarely, whether for operation, maintenance or service. The technology isthus user friendly, i.e. its use does not require training. In addition,the cost of employing the invented technology is also kept low becauseconsumables are unnecessary.

Unlike in situ detection methods, the invented technology is inexpensiveand even allows a more comprehensive analysis of airborne particles.Because aggregates of particles rather than individual particles aresubject to characterization, the technology does not requiresophisticated equipment like powerful lasers and very sensitive photoncounters. Therefore, the invented technology is more affordable. Inaddition, immobilization of particles makes possible prolonged analysisor multiple analyses of samples. Hence, the invention is compatible witha more thorough sample analysis and consequent increased reliability.

The invented technology allows affordable, automatic, and user friendlymonitoring of airborne particles. Consequently, prolonged monitoring ofa large number and variety of premises is feasible. Continuousmonitoring even of buildings at low risk of biohazard exposure mightmake a critical difference because noxious biologicals can havedevastating effects. Thus, the invention can minimize exposure ofpersons and expedite protective measures. Moreover, the technology lendsitself to integration with other types of monitoring technologies, forexample smoke, chemical, and/or radiological alarms, for comprehensiveenvironmental monitoring solutions. In sum, the invented technologypermits widespread adoption of airborne biological detectors, resultingin increased security of a large segment of the human population.

The examples presented below are provided as a further guide to apractitioner of ordinary skill in the art, and are not meant to belimiting in any way.

EXAMPLE

Detection of Aerosolized Fluorescent Particles Using a RegenerativeSurface

A regenerative surface air sampler based was constructed. The impactionplate was made of aluminum, and was shaped as a lobed cam with threeregenerative surfaces. Components of the system included an inertialimpactor, a fluorescence detector, and a felt wheel brush surfaceregenerator. The fluorescence detector was arranged essentially asdepicted in FIG. 5, with transmission characteristics of the dichroicmirror, excitation and emission filters as shown in FIG. 7. The UV LEDemission was specified to be about 375+/−3 nm.

Biological aerosol was simulated with a fluorescent powder (UVPN UVPowder sold by LDP, LLC (www.maxmax.com)). It was aerosolized by tappingan open envelope of the powder three times, releasing approximately 100milligrams of the powder into the air several feet away from the airinlet to the sensor.

Results of the test are shown in FIG. 8. As can be seen, the apparatusreliably detected releases of fluorescent particles. It is alsonoticeable that the baseline value varies slightly for each independentregenerative surface, suggesting that improved accuracy may be achievedusing surface specific averages. Note that the algorithm employed forthis example holds the baseline at a constant level for the next 10samples after an alarm.

All cited documents, including patents, patent applications, and otherpublications are incorporated herein by reference in their entirety.

Foregoing described embodiments of the invention are provided asillustrations and descriptions. They are not intended to limit theinvention to the precise form described. Other variations andembodiments are possible in light of above teachings, and it is thusintended that the scope of invention not be limited by this DetailedDescription, but rather by the following claims.

1. A device comprising: a sensor based on a regenerative surface airsampler, the sensor comprising: a regenerable collection surfaceconfigured to collect particles from the air; a surface regeneratorconfigured to remove particles from the regenerable collection surface,such that once regenerated, the regenerable collection surface cancollect additional particles from the air, and such that particlescollected before regeneration of the regenerable collection surface aresubstantially no longer present to contaminate particles collected afterthe regeneration; and an analyzer for evaluating the particles collectedon the regenerable collection surface; and a communication interfacecoupled to the sensor.
 2. The device according to claim 1, wherein thesensor is selected from the group consisting of biological, chemical,and radiological sensors.
 3. The device according to claim 1, whereinthe communication interface is selected from the group consisting of atransmitter, a transceiver, and an interface that is configured tocommunicate over an automation system network.
 4. The device accordingto claim 1, wherein the regenerable collection surface is part of animpaction plate.
 5. The device according to claim 1, wherein the sensorfurther comprises a spotting nozzle configured to direct an air streamtowards the regenerable collection surface, such that the resultingimpact of the air stream with the regenerable collection surfacegenerates a spot of particles on the regenerable collection surface. 6.The device according to claim 1, wherein the surface regeneratorcomprises at least one element selected from the group consistingessentially of: a brush that regenerates the regenerable collectionsurface by brushing away particles that were collected on theregenerable collection surface; a pad that regenerates the regenerablesurface by pressing against the regenerable collection surface whilethere is movement between the pad and the regenerable collection surfacerelative to each other, so as to remove particles that were collected onthe regenerable collection surface; and a wheel coupled to a motor thatregenerates the regenerable collection surface by pressing against theregenerable collection surface while the motor rotates the wheel, so asto remove particles that were collected on the regenerable collectionsurface.
 7. The device according to claim 1, further comprising abattery backup power supply.
 8. The device according to claim 1, furthercomprising a building, such that the device is incorporated into thebuilding.
 9. The device according to claim 1, further comprising anaircraft, such that the device is incorporated into the aircraft. 10.The device according to claim 1, wherein the sensor is capable to outputa positive response to the communication interface; and furthercomprising an air sampler coupled to the communication interface,wherein the air sampler can be activated by the positive responsecapture at least one sample of airborne particles.
 11. The device ofclaim 1, wherein the surface regenerator comprises at least one elementselected from the group consisting essentially of: a nozzle configuredto direct high velocity air towards the regenerable collection surfaceto dislodge particles deposited thereon; a blade configured to scrapethe regenerable collection surface to dislodge particles depositedthereon; means for electrostatically charging the collection surface, sothat a static charge disperses the particles that were depositedthereon; means for directing energy to the particles collected upon theregenerable collection surface to dislodge particles deposited thereon;and means for directing energy to the regenerable collection surface todislodge particles deposited thereon.
 12. The device of claim 1, whereinthe sensor further comprises at least one element selected from thegroup consisting of: a particle concentrator configured to increase aconcentration of airborne particles within a desirable size range in anair stream from which the regenerable collection surface collectsparticles; and a size-selective inlet configured to precondition airfrom which particles are to be collected by the regenerable collectionsurface by removing particles from the air that have a size greater thana predefined size.
 13. The device of claim 1, wherein the sensor furthercomprises a mechanically-based homing sensor that positions theregenerable collection surface relative to a selected component, theselected component comprising at least one component selected from thegroup consisting essentially of: a spotting nozzle configured to deposita spot of particles on the regenerable collection surface; the analyzer;the surface regenerator; and a liquid coating applicator used to apply aliquid to the regenerable collection surface, to moisten the regenerablecollection surface prior to collecting the particles, thereby enhancinga collection efficiency of the regenerable collection surface.
 14. Thedevice of claim 1, wherein the sensor further comprises a processorcoupled to the analyzer, the processor being logically configured todetermine a concentration of biological particles collected on theregenerable collection surface, and to activate an alarm signal when theprocessor determines that the concentration of biological particlescollected on the regenerable collection surface exceeds a predeterminedvalue.
 15. An air monitoring system comprising: a sensor that includes:a regenerable collection surface configured to collect particles fromthe air, to provide sample particles; a surface regenerator configuredto remove particles from the collection surface, such that onceregenerated, the regenerable collection surface can collect additionalparticles from the air, particles that were collected beforeregeneration of the regenerable collection surface being substantiallyremoved by the surface regenerator to avoid contaminating particlescollected after the regeneration; and an analyzer configured todetermine characteristics of the particles collected on the regenerablecollection surface; a communication interface configured to enable theair monitoring system to be coupled to a network; and a controllercoupled to the sensor, the controller being configured to cyclicallyimplement a plurality of functions, including: directing airborneparticles so that they are deposited on the regenerable collectionsurface to form a spot; analyzing the particles forming the spot;transmitting a signal over the communication interface when the analysisindicates the particles represent a potential threat; and activating thesurface regenerator to regenerate the regenerable collection surfaceafter the particles have been analyzed.
 16. An air monitoring systemcomprising: a sensor based on a regenerative surface air sampler, thesensor comprising: a regenerable collection surface configured tocollect particles from the air; a surface regenerator configured toremove particles from the regenerable collection surface, such that onceregenerated, the regenerable collection surface can collect additionalparticles from the air, and such that particles collected beforeregeneration of the regenerable collection surface are substantially nolonger present on the regenerable collection surface to contaminateparticles collected after the regenerable collection surface isregenerated; and an analyzer for evaluating the particles collected onthe regenerable collection surface, in order to determine if thecollected particles represent a potential threat; and a controllercommunicatively coupled to the sensor, the controller being configuredto selectively actuate the surface regenerator to regenerate theregenerable collection surface.
 17. The system according to claim 16,wherein the sensor is selected from the group consisting of dumbsensors, smart sensors, and intelligent sensors.
 18. The systemaccording to claim 16, wherein the controller configured to actuate atleast one other component in response to information received from thesensor.
 19. The system according to claim 16, wherein the system isassociated with air management equipment.
 20. A network comprising: asensor based on a regenerative surface air sampler, the sensorcomprising: a regenerable collection surface configured to collectparticles from the air; a surface regenerator configured to removeparticles from the regenerable collection surface, such that once thusregenerated, the regenerable collection surface can collect additionalparticles from the air, and such that particles collected beforeregeneration of the regenerable collection surface are substantially nolonger present on the regenerable collection surface to contaminateparticles collected after the regeneration; and means for collectingdata corresponding to the particles collected on the regenerablecollection surface; a transceiver for communicating over an automationsystem network; at least one actuator; an air management componentcoupled to the actuator; and a controller communicatively coupled to thesensor, the transceiver, and the actuator, the controller beingconfigured to implement a plurality of functions, including: analyzingparticles collected on the regenerable collection surface using datacollected by the sensor; transmitting a signal to the automation systemnetwork using the transceiver when the analysis indicates the particlesrepresent a potential threat; and activating the surface regenerator toregenerate the regenerable collection surface after the particles havebeen analyzed.
 21. The network according to claim 20, wherein thecontroller actuates the air management component based on informationreceived from the sensor.
 22. The network according to claim 20, whereinthe surface regenerator comprises at least one element selected from thegroup consisting essentially of: a brush that regenerates theregenerable collection surface by brushing away particles that werecollected on the regenerable collection surface; a pad that regeneratesthe regenerable surface by pressing against the regenerable collectionsurface while there is relative movement between the pad and theregenerable collection surface, so as to remove particles that werecollected on the regenerable collection surface; and a wheel coupled toa motor that regenerates the regenerable collection surface by pressingagainst the regenerable collection surface while the motor rotates thewheel, so as to remove particles that were collected on the regenerablecollection surface.
 23. The network according to claim 20, wherein theair management component is selected from the group consisting of asample capture device, a sample analysis device, an air duct damper, anda particle counter.
 24. A system comprising: a sensor based on aregenerative surface air sampler, the sensor comprising: a regenerablecollection surface configured to collect particles from the air; asurface regenerator configured to remove particles from the regenerablecollection surface, such that once regenerated, the regenerablecollection surface can collect additional particles from the air, andsuch that particles collected before regeneration of the regenerablecollection surface are substantially no longer present on theregenerable collection surface to contaminate particles collected afterregeneration of the regenerable collection surface; and an analyzerconfigured to collect data corresponding to the particles collected onthe regenerable collection surface; a transceiver for communicating overan automation system network; and a controller communicatively coupledto the sensor and the transceiver, the controller being configured toimplement a plurality of functions, including: analyzing data collectedby the sensor corresponding to the particles collected on theregenerable collection surface to determine if the particles represent apotential threat; transmitting a signal to the automation system networkusing the transceiver when the analysis indicates the particlesrepresent a potential threat; and activating the surface regenerator toregenerate the regenerable collection surface after the particles havebeen analyzed.
 25. The system according to claim 24, wherein thecontroller communicates via at least one technique selected from thegroup consisting of a BACnet protocol, a wireless communication, an RFlink to an RF link network, and a wired link.
 26. The system accordingto claim 24, wherein the surface regenerator comprises at least oneelement selected from the group consisting essentially of: a brush thatregenerates the regenerable collection surface by brushing awayparticles that were collected on the regenerable collection surface; apad that regenerates the regenerable collection surface by pressingagainst the regenerable collection surface while the pad and theregenerable collection surface move relative to each other, so as toremove particles that were collected on the regenerable collectionsurface; and a wheel coupled to a motor for regenerating the regenerablecollection surface by pressing against the regenerable collectionsurface while the motor rotates the wheel, so as to remove particlesthat were collected on the regenerable collection surface.
 27. Thesystem according to claim 24, wherein the sensor further comprises amechanically-based homing sensor that positions the regenerablecollection surface relative to a specific component, the specificcomponent comprising at least one component selected from the groupconsisting essentially of: a spotting nozzle configured to deposit aspot of particles on the regenerable collection surface; the analyzer;the surface regenerator; and a liquid coating applicator used to apply aliquid to the regenerable collection surface.
 28. A method ofconstructing a network of sensors, the method comprising adding a sensorbased on a regenerative surface air sampler to the network, wherein thesensor comprises: a regenerable collection surface configured to collectparticles from the air; and a surface regenerator configured to removeparticles from the regenerable collection surface, such that once theregenerable collection surface is regenerated, the regenerablecollection surface can collect additional particles from the air, andsuch that particles collected before regeneration of the regenerablecollection surface are substantially no longer present on theregenerable collection surface to contaminate particles collected afterthe regeneration of the regenerable collection surface.
 29. The methodaccording to claim 28, where the network comprises a smoke or firesensor.
 30. A method of controlling ambient air quality, the methodcomprising: sampling ambient air with at least one sensor based on aregenerative surface air sampler, the sensor comprising: a regenerablecollection surface configured to collect particles from the air; asurface regenerator configured to remove particles from the regenerablecollection surface, such that once regenerated, the regenerablecollection surface can collect additional particles from the air, andsuch that particles collected before regeneration of the regenerablecollection surface are substantially no longer present to contaminateparticles collected after the regeneration of the regenerable collectionsurface; and means for determining if the particles collected on theregenerable collection surface represent a potential threat to airquality; and upon receiving an indication of a probable threat from thesensor, performing a responsive step.
 31. The method according to claim30, wherein the responsive step comprises at least one step selectedfrom the group consisting essentially of actuating an air managementcomponent, activating at least one sampler specific sensor, issuing awarning signal, and transmitting an alert signal to facility management.32. The method according to claim 30, further comprising the step ofanalyzing particles on the regenerable collection surface to determinewhether or not an indication of a probable threat exists.
 33. The methodaccording to claim 32, wherein after the step of analyzing theparticles, further comprising the step of activating the surfaceregenerator to remove particles from the regenerable collection surface,such that once regenerated, the regenerable collection surface cancollect additional particles from the air, and such that particlescollected before regeneration of the regenerable surface aresubstantially no longer present to contaminate particles collected afterthe regeneration.
 34. The method according to claim 30, wherein theresponsive step comprises the step of transmitting an alert signal to afire department or law enforcement agency.
 35. Apparatus configured tocollect airborne particles, comprising: a sensor based on a regenerativesurface air sampler, the sensor comprising: a regenerable collectionsurface configured to collect particles from the air; and a surfaceregenerator configured to remove particles from the regenerablecollection surface, such that once regenerated, the regenerablecollection surface can collect additional particles from the air, andsuch that particles collected before regeneration of the regenerablecollection surface are substantially no longer present to contaminateparticles collected after the regeneration; and a communicationinterface coupled to the sensor.
 36. A method for continuouslymonitoring airborne particles, the method repetitively carrying out aplurality of cycles, each cycle comprising the steps of: depositingparticles that were airborne on a regenerable collection surface;analyzing the particles that were deposited on the regenerablecollection surface; when analysis indicates that the particles depositedrepresent a potential threat, transmitting a signal indicative of thepotential threat over a network; and regenerating the regenerablecollection surface to substantially remove the particles that weredeposited thereon during a previous cycle.
 37. The method of claim 36,wherein the step of depositing particles on the regenerable collectionsurface comprises the step of depositing the particles to form a spot.38. The method of claim 36, wherein the step of regenerating thecollection surface comprises at least one step selected from the groupof steps consisting essentially of: brushing the regenerable collectionsurface, to dislodge the particles deposited on the regenerablecollection surface; pressing a pad against the regenerable collectionsurface while there is relative motion between the pad and theregenerable collection surface, to remove the particles deposited on theregenerable collection surface; pressing a wheel against the regenerablecollection surface while there is relative motion between the wheel andthe regenerable collection surface, to remove the particles deposited onthe regenerable collection surface; directing high velocity air towardsthe regenerable collection surface to dislodge the particles depositedon the regenerable collection surface; electrostatically charging theregenerable collection surface to electrostatically disperse theparticles deposited on the regenerable collection surface; and directingenergy to the particles collected upon the regenerable collectionsurface to dislodge the particles deposited on the regenerablecollection surface.
 39. The method of claim 36, further comprising thestep of verifying that the step of regenerating the regenerablecollection surface has substantially removed the particles that werepreviously deposited before starting to deposit particles on theregenerable collection surface in a next cycle.
 40. The method of claim39, wherein the step of analyzing the particles that were depositedcomprises measuring fluorescence properties of the deposited particles,and the step of verifying that the step of regenerating the regenerablecollection surface has substantially removed the particles that werepreviously deposited comprises the steps of: determining a backgroundfluorescence level for the regenerated collection surface; and comparingthe background fluorescence level with predetermined criteria, such thatif the background fluorescence level does not substantially satisfy thepredetermined criteria, the step of regenerating is repeated beforestarting to deposit particles on the regenerable collection surface in anext cycle, until the background fluorescence level substantiallysatisfies the predetermined criteria.
 41. The method of claim 36,wherein the step of analyzing the particles that were depositedcomprises at least one step selected from the group consisting of:pre-treating the particles that were deposited by performing plasmalysing, adding a matrix solution, and measuring a mass spectra of theparticles that were deposited and pretreated, using mass spectrometry;and measuring an autofluorescence of any bio-molecules that may bepresent in the particles that were deposited to obtain a biologicalsignature of the particles, the biological signature being obtainedusing the steps of: determining an average value and a standarddeviation based on previously obtained estimates of the concentration ofbiological particles; comparing the estimated concentration to theaverage value; and transmitting the signal if the estimatedconcentration exceeds a sum of the average value and a product of apredetermined factor and the standard deviation.
 42. The method of claim36, wherein the method steps are implemented by a plurality of sensorscoupled together to form a network, to enable air monitoring over awider area than that monitored using a single sensor.
 43. The method ofclaim 36, wherein the step of transmitting the signal indicative of theresults over the network comprises at least one step selected from thegroup of steps consisting essentially of: activating an alarm signaldirected to a designated party; actuating an air management component;producing a warning signal; moving a damper in an air duct; transmittingan alarm signal to a fire department; transmitting an alarm signal to alaw enforcement agency; and transmitting an alarm signal to a managemententity responsible for managing a facility.